1. Field of the Invention
The present invention relates to a control device for a heat roller, and especially relates to a control device configured to control heating carried out with regard to a heat roller.
2. Description of the Related Art
As for an image formation apparatus such as a printer, a copier, etc., during a process of fusing (i.e. fixing) a toner image to a recording medium such as a piece of paper, etc., by utilizing heat treatment, it is necessary to carry out control with regard to a heat roller (also called “fuser roller”) so as to avoid damage to the image formation apparatus, caused by overheating of the heat roller.
In conventional techniques, a control device such as a CPU, etc., is used to carry out monitoring with regard to temperature, and based on the detected temperature, to perform corresponding temperature adjustment control with regard to the heat roller. In this control process, if it is detected that the temperature is too high, then power feeding to the heat roller for heating is cut off.
In addition, aside from software stored in a control device such as a CPU, etc., hardware such as a circuit, etc., may also be utilized to forcibly cut off control carried out with regard to the heat roller. In this kind of hardware, for example, a circuit is usually formed of a comparator and a latch. The comparator is used to carry out comparison between voltage obtained from a temperature sensor and reference voltage of high temperature malfunction. If the voltage obtained from the temperature sensor (i.e., the voltage corresponding to the current temperature obtained by the temperature sensor) exceeds a predetermined reference voltage for high temperature malfunction (i.e., the voltage corresponding to a high temperature threshold value TH), the comparator outputs a high temperature malfunction signal, and then the latch latches this state and cuts off power feeding to the heat roller.
After the image formation apparatus is stopped and restarted, in order to prevent continuous heating of the heat roller, when the high temperature malfunction signal is generated, it is necessary to store a high temperature malfunction code into an electrically erasable programmable read-only memory (EEPROM) in general. Once the high temperature malfunction code is stored into the EEPROM, the image formation apparatus cannot start according to a normal start method so as to avoid damage to the image formation apparatus that would be caused by the further heating of the heat roller. If the high temperature malfunction code stored in the EEPROM needs to be erased, it is necessary to artificially carry out an erase operation.
Furthermore, due to influence of noise caused by, for example, static electricity, a false operation may occur in the above described circuit so as to cause wrong detection of high temperature malfunction. For example, in a case where high temperature malfunction does not exist, it is possible to detect temperature within a normal temperature range as high temperature due to influence of noise, etc., so as to cause wrong detection of high temperature malfunction, as shown in (b) of FIG. 1. As a result, although high temperature malfunction does not exist in the heat roller, it is possible for a normal condition to be detected as a high temperature malfunction; then, since a high temperature malfunction code is written into the EEPROM, it is necessary to artificially carry out a dedicated operation to erase the high temperature malfunction code. This may cause inconvenience on use.
In the conventional techniques, for example, in the below cited reference No. 1, a method of detecting high temperature malfunction is disclosed. However, this reference does not mention how to avoid a problem of influence caused by noise occurring in a circuit.
In order to remove this kind of influence possibly existing in a circuit, and to further improve accuracy of high temperature malfunction detection, it is necessary to develop a more stable and reliable control device for the heat roller.
In addition, although those people skilled in the art may know that it is possible to employ a noise filter to remove noise so as to avoid this kind of problem, this may call for hardware and cost increase.
Cited Reference No. 1: Japan Patent Application Publication No. 2004-77595